Coach Steve Spagnuolo has not decided whether Bulger should be placed on injured reserve, which would end his season. Spagnuolo said Bulger would not need surgery.
"It's just crutches. He'll have to say off it for a while," Spagnuolo said in a St. Louis Post-Dispatch report.
Bulger was hurt Sunday in a 21-13 Rams loss to Arizona.
With Bulger out, Kyle Boller becomes the starting quarterback and Keith Null is the backup.
The Rams are 1-9 this season. Bulger has played in all but one game, passing for 1,459 yards with five touchdowns and six interceptions.
Puzzle-maker slips 'Murdoch Is Evil' into Rupert Murdoch's Sunday Telegraph
Reindeer recovered after escaping from Santa during lighting ceremony